The aromatic diamine 2,2-bis(4-aminophenyl)hexafluoropropane is a known product which is useful in the preparation of polyimides and polyamides These polymers are known in the literature; see e.g. U.S. Pat. No. 3,356,648 and U.S. Pat. No. 3,328,352. These polymers possess high thermal stability, enhanced light transparency, and improved processing characteristics. These properties give such polymers application in areas where high service temperature stability is required, such as aircraft composites and high temperature shaped parts and films. They are prepared by reacting the aromatic diamine with a dianhydride or dicarboxylic acid chloride to produce the polyimide or polyamide, respectively
The literature describes several methods to prepare the 2,2-bis(4-aminophenyl)hexafluoropropane intermediate. U.S. Pat. No. 3,328,352 teaches its preparation by the direct condensation of aniline with hexafluoroacetone in the presence of an aluminum chloride catalyst The reaction conditions are severe and the reported yield is very low--approximately 26 percent.
Another literature preparation is reported in Chemical Abstracts, 65, 185236. This method involves the application of the Curtius rearrangement of the diacyl azide prepared from the corresponding dicarboxylic acid chloride; i.e., 2,2-bis(4-chlorocarbonylphenyl)hexafluoropropane. However, here again the reported yield is low--only 42 percent.
Another literature preparation is reported in U.S. Pat. No. 3,310,573. This method involves the application of the Schmidt reaction [R. F. Schmidt, Ber., 57, 704 (1924)] on the 2,2-bis(4-carboxylphenyl)hexafluoropropane. Here, the dicarboxylic acid is reacted with hydrazoic acid to give the desired diamine directly. The yield again is reported "poor" with no specific value reported.
The low yields of the above literature reports apparently prompted another approach to produce the desired diamine. Lau et al [J. Polymer Science, Polymer Chemistry Edition, 20, 2381 (1982)] reported its preparation from 2,2-bis(4-hydroxyphenyl)hexafluoropropane. Here, the commercially available dihydroxy compound was reacted with 2-chloro-4-phenylquinazoline to give the bis quinazoline condensation product which was then thermally rearranged to the quinazolinone which was then hydrolzyed to the diamine. Again, the reported yield was low--just 16.5 percent. In addition the method requires severe reaction conditions and a chromatographic purification of the product which is not readily adapted to a commercial manufacturing process.
It is the object of this invention to produce high purity 2,2-bis(4-aminophenyl)hexafluoropropane in high yield from readily available materials by a simple, commercially feasible process.